Hi DrLuigi,

I haven't used ABS much since I prefer PLA but still I might suggest you to use closed heated chamber.
If is is possible add some acrylic glass sheets around your working area thus the heat coming from heated bed will be trapped
inside and temperature will be significantly higher than the surrounding.

Another pretty simple thing you can try is to set skirt to the same height as your printed part is. That might also help to prevent
cooling of the perimeters.

Hope it helps

- Filip